This invention relates to current ratioing and, more particularly, to current splitter circuits for providing multiple output currents having precise ratios with respect to each other. Further, the present invention pertains to a resistive trim technique such that the ratios of the output currents may be adjusted wherein the adjusted ratios are temperature independent.
Current splitting techniques are known. One method realized to provide output currents having a predetermined ratio with respect to each other is the common current mirror circuit. The current mirror comprises a diode-connected transistor coupled in a parallel current path to the base-emitter conduction path of a transistor of like conductivity type. An input current supplied to the diode is mirrored through the collector-emitter conduction path of the transistor as understood. By area ratioing the emitters of the two transistors the ratio of the current flow through the transistor can be set with respect to the input current flow through the diode-connected transistor. The current ratio can also be set by utilizing trimmable resistors in the respective emitter conduction paths of the two transistors. By trimming one or the other or even both resistors the current ratios can be adjusted.
A problem with some prior art current splitters is that even though the current ratios can be precisely set at ambient temperature by trimming of resistors the ratios are not temperature independent. Thus, as temperature varies the current ratios will not remain constant but will also vary. In many applications this is very undesirable.
Hence, a need exists for a current splitter for providing currents having adjustable current ratios that are temperature independent.